1. Technical Field of the Invention
A subject-matter of the invention is the use of an effective amount of a pyridinedicarboxylic acid derivative or of one of its salts in a composition intended to induce and/or stimulate the growth of human keratinous fibers and in particular of human hair and eyelashes and/or to slow down their loss. In addition, it relates to a cosmetic treatment process intended to stimulate the growth of human keratinous fibers, such as the hair and eyelashes, and/or to retard their loss.
2. Description of the Prior Art
Hair growth and its replacement are mainly determined by the activity of the hair follicles and their matrix environment. Their activity is cyclical and comprises essentially three phases, namely the anagenic phase, the catagenic phase and the telogenic phase.
The anagenic phase (active or growth phase), which lasts several years and during which the hair grows longer, is followed by a very short and transitory catagenic phase, which lasts a few weeks, and then by a telogenic phase or resting phase, which lasts a few months.
At the end of the resting period, the hair falls out and another cycle recommences. The head of hair is thus constantly replaced and, of the approximately 150,000 hairs which a head of hair comprises, approximately 10% are at rest and will be replaced in the months to come.
Natural hair loss can be estimated, on average, at a few hundred individual hairs per day for a normal physiological state. This process of constant physical replacement undergoes a natural change with aging, the hair becomes finer and its cycles shorter.
In addition, various causes can result in significant hair loss, whether temporary or definitive. Hair loss, in particular alopecia, is essentially due to disturbances in hair replacement. These disturbances result first in the acceleration in the frequency of the cycles, at the expense of the quality of the hair and then of their quantity. The bulbs gradually become smaller and, at the same time, the latter become isolated by gradual thickening of the perifollicular collagen matrix and of the external connective tissue sheath. Revascularization about the hair follicle is therefore rendered more difficult cycle after cycle. Individual hairs regress, becoming smaller until no more than an unpigmented down, and this phenomenon results in a gradual thinning of the head of hair.
Areas are preferentially affected, in particular the temporal or frontal regions in men and, in women, diffuse alopecia of the vertex is observed.
The term “alopecia” also covers a whole family of conditions of the hair follicle having, as final consequence, the definitive loss, partial or general, of the hair. It relates more particularly to androgenic alopecia. In a large number of cases, early hair loss occurs in genetically predisposed individuals. This is then androchronogenetic alopecia; this form of alopecia concerns men in particular.
Furthermore, it is known that certain factors, such as a hormone imbalance, a physiological stress or malnutrition, can accentuate the phenomenon. In addition, hair loss or detrimental change can be related to seasonal phenomena.
Generally, any factor which influences these processes, namely the acceleration in the frequency of the cycles, the gradual reduction in size of the bulbs, the gradual thickening of the perifollicular collagen matrix, the thickening of the external connective tissue sheath and the reduction in vascularization, will have an effect on the growth of the hair follicles.